A common problem associated with window and door constructions is the accumulation of water with the sill structure during storm conditions. Water will collect on the inside of the sill plate due to leakage around or under the movable sash or because the sash did not properly seal against the sill and vertical frame members.
Prior art efforts to mitigate the accumulation of water include providing a series of vents with flaps on an exterior face of the top sill or head of the window. This permits outside air pressure to enter the head. A series of weep or drainage holes are provided in the bottom sill to allow entrapped water to be forced out of the sill under pressure from the vent.
While the above system performs reasonably well at lower pressures, it becomes increasingly difficult to drain entrapped water at higher pressures, namely during storm conditions. For optimal drainage a window, door or wall frame would preferably vent to a neutral pressure. However, when the prior art system is subjected to the relatively high pressures such as those encountered during windy and rainy weather, the cavity inside the window or door sill is at that same pressure and draining becomes difficult if not impossible. This is best shown in FIG. 5 of the drawings which illustrates the prior art pressure imbalance and resultant accumulation of water within the sill. In view of the fact that storm conditions involve large amounts of water; a need has existed in the art for a building cavity ventilation system that functions under varying conditions including those involving high exterior pressures. Further, the vents provided in the top sill of the prior art window or doors are predisposed to allow entry of excess water into sill which undesirably increases the quantity of water that needs to be drained.